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Difficulty: MediumSpanning Tree Protocol Operations

A network switch interface configured with legacy IEEE 802.1D Spanning Tree Protocol (STP) has just experienced a physical link bring-up event. In what precise chronological order will the port transition through its operational states from initial activation to active data forwarding?

  1. 1Blocking State
  2. 2Listening State
  3. 3Learning State
  4. 4Forwarding State

Answer

The correct operational order of IEEE 802.1D STP port states from initial link bring-up to full operation is Blocking State, Listening State, Learning State, and Forwarding State.
Under IEEE 802.1D STP, a switch interface transitions through four distinct operational states upon physical link up to guarantee loop avoidance. It begins in Blocking (discarding traffic and listening for BPDUs), transitions after the forward delay timer to Listening (exchanging BPDUs to determine roles), moves after a second forward delay timer to Learning (populating MAC tables without forwarding data), and finally settles in Forwarding (actively transmitting user frames and BPDUs).

Step-by-Step Solution

1
Identify the state immediately entered upon physical link up.
The port initializes in the Blocking State.
STP defaults to Blocking to safeguard the Layer 2 domain from transient loops while initial BPDU exchange occurs.
2
Determine the state focused on topology determination and role negotiation.
The port transitions to the Listening State.
During Listening, the port active participates in BPDU transmission and election processes without altering MAC tables or forwarding data.
3
Identify the state focused on building layer 2 forwarding tables prior to frame delivery.
The port transitions to the Learning State.
Learning allows the switch to populate its MAC address table from source addresses to prevent unnecessary unicast flooding when data forwarding begins.
4
Identify the final fully operational state.
The port enters the Forwarding State.
In Forwarding, all loop management checks are complete, enabling full ingress and egress user payload traffic handling.

Key Concept

IEEE 802.1D Spanning Tree Protocol Port State Transitions
Estimated Time:1m 30s
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Topics

Spanning Tree Protocol Operations

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